In recent years, there have been put to practical use services called MBMS for simultaneously distributing multimedia data (hereinafter referred to as MBMS data) such as movie and music data to a plurality of mobile terminals by way of broadcast or multicast transmission.
FIG. 1 shows the configuration of a mobile communication system which is capable of providing MBMSs. The configuration shown in FIG. 1 is stipulated by 3GPP (3rd Generation Partnership Projects).
As shown in FIG. 1, the mobile communication system includes UTRAN (Universal Terrestrial Radio Access Network) 10 connected to CN (Core Network) 40. CN 40 has SGSN (Serving GPRS Support Node) 50 at its junction with UTRAN 10.
UTRAN 10 comprises RNCs (Radio Network Controllers) 20 and nodes B (base station apparatus) 30. Each node B 30 serves to cover a cell or a plurality of cells, and is connected to UE (User Equipment) 60 by a radio interface.
When the mobile communication system constructed as described above starts to provide an MBMS, RNC 20 sends an MBMS MODIFIED SERVICES INFORMATION message to UE 60 that is interested in the MBMS in order to notify that the MBMS will be started, and thereafter starts distributing MBMS data. When other changes are to be made to the MBMS, e.g., when the MBMS is to be ended, RNC 20 also sends an MBMS MODIFIED SERVICES INFORMATION message to UE 60.
According to one method of sending an MBMS MODIFIED SERVICES INFORMATION message, an MCCH (MBMS point-to-multipoint Control Channel) is used as disclosed in Patent document 1, for example. Generally, while UE 60 is establishing an individual channel (Cell_DCH), UE 60 is able to receive an individual channel DPDCH, but unable to receive a common channel S-CCPCH. The MCCH is mapped onto the S-CCPCH. Therefore, while UE 60 is establishing an individual channel, it cannot receive the MCCH.
According to another method of sending an MBMS MODIFIED SERVICES INFORMATION message, an MICH (MBMS notification Indicator Channel) is used if UE 60 supports the MICH. However, UE 60 does not notify RNC 20 of whether or not it supports the MICH.
Therefore, RNC 20 needs to send an MBMS MODIFIED SERVICES INFORMATION message to UE 60 while it is establishing an individual channel, on a DCCH (Dedicated Control Channel).
In advance, UE 60 sets an MBMS selected from the MBMSs provided by network operators in an MBMS MODIFICATION REQUEST message, and sends the MBMS MODIFICATION REQUEST message to RNC 20. Based on the MBMS MODIFICATION REQUEST message from UE 60, RNC 20 determines the MBMS in which UE 60 is interested in.
Related methods of sending an MBMS MODIFIED SERVICES INFORMATION message and an MBMS MODIFICATION REQUEST message will be described below.
(1) Method of Sending an MBMS MODIFIED SERVICES INFORMATION Message:
It is assumed that RNC 20 is triggered by the reception of notification of the start of the MBMS from CN 40 to send an MBMS MODIFIED SERVICES INFORMATION message representing the start of an MBMS to UE 60.
RNC 20 also sends an MBMS MODIFIED SERVICES INFORMATION message when it receives notification of any of other changes made to the MBMS from CN 40.
As shown in FIG. 2, when RNC 20 receives an MBMS SESSION START message representative of the start of the MBMS from CN 40 in step 1201, RNC 20 analyzes a cell serving as a service area of the MBMS and establishes radio resources in step 1202.
Then, in step 1203, RNC 20 searches a memory thereof for UE 60 which is interested in the MBMS.
In step 1204, RNC 20 determines whether or not UE 60 searched for in step 1203 has been establishing an individual channel.
If UE 60 that was discovered in step 1203 is establishing an individual channel, then RNC 20 sends an MBMS MODIFIED SERVICES INFORMATION message to UE 60 on a DCCH in step 1205.
If UE 60 that was searched for in step 1203 has not been establishing an individual channel, then RNC 20 sends an MBMS MODIFIED SERVICES INFORMATION message to UE 60 on an MCCH or an MICH.
(2) Method of Sending an MBMS MODIFICATION REQUEST Message:
According to the 3GPP, RNCs 20, nodes B 30, the cells, and the frequency bands can be shared by a plurality of network operators in a network configuration such as an MOCN (Multi-Operator Core Network), a GWCN (Gateway Core Network), etc. Such an environment is called a network sharing environment.
In the network sharing environment, RNC 20 sets a list of network operators (Multiple PLMN List) in an MIB (Master Information Block) of announcement information as system information, and sends the announcement information to UE 60.
In the network sharing environment, UE 60 can set an MBMS selected from the MBMSs provided by the network operators in an MBMS MODIFICATION REQUEST message according to an MBMS Selected Service Info parameter, and can send the MBMS MODIFICATION REQUEST message to RNC 20. For example, an MBMS selected by UE 60 based on the selection of a channel on Mobile-TV is notified to UTRAN 10. Service ID (identification information) is defined for each of the MBMS provided by the network operators.
UE 60 sets the selected MBMS in the MBMS MODIFICATION REQUEST message by notifying the network operator which provides the MBMS according to any one of processes (A) through (C) shown below.
(A) Notifying the same network operator ID as a network operator ID (identification information) in the Multiple PLMN List in the MIB.
(B) Notifying a network operator ID in the Multiple PLMN List in the MIB.
(C) Sending a network operator ID itself independently of the MIB.
Since no standards clearly show which of the processes (A) through (C) should be used by UE 60, the process to be used depends on how UE 60 is implemented.
However, the above methods of sending an MBMS MODIFIED SERVICES INFORMATION message and an MBMS MODIFICATION REQUEST message suffer the following problems:
(1) The Problems of the Method of Sending an MBMS MODIFIED SERVICES INFORMATION Message:
As shown in FIG. 3, while UE 60 is establishing an individual channel, UE 60 can be in a handover state having a radio link to a plurality of cells (in a state of soft handover to a plurality of cells).
For receiving MBMS data of an MBMS, UE 60 reads MBMS control information about the MBMS (e.g., information as to which cell's MBMS data are to be received and combined) on an MCCH, and thereafter receives the MBMS data based on the MBMS control information read on the MCCH. The cell from which the MBMS control information is read on the MCCH is referred to as an MBMS control cell. If UE 60 is in a handover state, then any one of a plurality of cells to which a radio link has been established by the handover is a candidate for an MBMS control cell. The cell selected by UE 60 as an MBMS control cell is not notified to RNC 20.
For example, it is assumed that, as shown in FIG. 3, UE 60 is simultaneously connected to cell 1, cell 2, and cell 3 by handover, selects cells 2 as an MBMS control cell, and receives the MBMS control information from the MBMS control cell on the MCCH. It is also assumed that cell 2 has already started service 2 of the MBMS and cell 3 has also already started service 3 of the MBMS, and that service 1 of the MBMS is started by an MBMS SESSION START message from CN 40, and the service area of service 1 covers cell 1, cell 4, cell 5, and cell 6, i.e., service 1 is started by cell 1, but not by cell 2 and cell 3.
RNC 20 sends an MBMS MODIFIED SERVICES INFORMATION message about service 1 to UE 60. However, since the MBMS MODIFIED SERVICES INFORMATION message is unable to send information about cells, UE 60 may malfunction.
This problem will be described in detail below.
UE 60 has selected cell 2 as an MBMS control cell, and can read only MBMS control information about cell 2 on the MCCH. Stated otherwise, UE 60 is unable to read MBMS control information about cell 1 on the MCCH, and, as a result, is unable to receive MBMS data according to service 1.
Since UE 60 is simultaneously connected to cell 1, cell 2, and cell 3 by handover, RNC 20 sends an MBMS MODIFIED SERVICES INFORMATION message about service 1 to UE 60 on the DCCH through cell 1, cell 2, and cell 3. At this time, as described above, the MBMS MODIFIED SERVICES INFORMATION message sent from RNC 20 to UE 60 is unable to send information about cells.
Therefore, UE 60 cannot recognize which cell the MBMS MODIFIED SERVICES INFORMATION message about service 1 has been sent to, and hence cannot determine which cell has started service 1.
As a consequence, a problem arises in that UE 60 processes the MBMS MODIFIED SERVICES INFORMATION message about service 1 and attempts to receive MBMS data according to service 1 though it is unable to receive MBMS data according to service 1.
Depending on its ability, UE 60 may not simultaneously receive MBMS data according to a plurality of MBMS and may not simultaneously receive MBMS data according to MBMS and services other than MBMS (ordinary packet services). When such UE 60 receives the MBMS MODIFIED SERVICES INFORMATION message about service 1 on the DCCH, it prioritizes service 1 and MBMS and services other than MBMS which have currently been received.
If the priority of service 1 is high, then a problem also arises in that UE 60 finishes the MBMS and services other than MBMS which have currently been received that have lower priorities, thus performing a bearer releasing process, according to a Deactivate PDP context request process in order to receive MBMS data according to service 1.
(2) The Problems of the Method of Sending an MBMS MODIFICATION REQUEST Message:
As described above, the processes (A) through (C) are available for UE 60 to notify the network operator which provides selected the MBMS in the MBMS MODIFICATION REQUEST message.
The processes (A), (B) are processes for simplifying and notifying a network operation ID depending on the announcement information. However, since the MBMS MODIFICATION REQUEST message sent from UE 60 to RNC 20 is unable to send information about cells, RNC 20 may malfunction in the network sharing environment according to the processes (A), (B).
This problem will be described in detail below.
FIG. 4 shows a network sharing configuration wherein SGSNs 50 of three network operators are connected to single RNC 20. FIG. 4 shows the relationship between SGSNs 50 and RNC 20, and FIG. 5 shows which network operator controls each cell.
As shown in FIG. 5, a case will be analyzed in which RNC 20 as a higher-level apparatus is controlled by cell 1 of network operator 1, cell 2 of network operator 2, and cell 3 of network operator 3, i.e., RNC 20 is shared by a plurality of network operators. In this case, it is assumed that a service having service ID=1 of network operator 1 is being carried out by cell 1, a service having service ID=1 of network operator 2 is being carried out by cell 2, and a service having service ID=1 of network operator 3 is being carried out by cell 3. However, inasmuch as MBMS services have service IDs defined for respective network operators, services having one service ID may not be necessarily the same as each other provided that their network operators IDs are different from each other. It is also assumed that UE 60 is simultaneously connected to cell 1, cell 2, and cell 3 by handover and reads announcement information from cell 2.
In the case shown in FIG. 5, it is assumed that UE 60 has sent an MBMS MODIFICATION REQUEST message to RNC 20 according to the process (A) or (B) in steps 1601, 1602 shown in FIG. 6.
However, as described above, the MBMS MODIFICATION REQUEST message is unable to send information about cells.
Therefore, RNC 20 cannot recognize from the MBMS MODIFICATION REQUEST message from which cell UE 60 is reading announcement information. Consequently, when UE 60 notifies a network operator ID according to the simplified process (A) or (B), RNC 20 may possibly mistake the network operator selected by UE 60 as the network operator of cell 1 or cell 3 rather than cell 2.
If RNC 20 mistakes the network operator selected by UE 60, then RNC 20 cannot properly notify that the MBMS has been changed to UE 60.
As described above, the MBMS MODIFIED SERVICES INFORMATION message and the MBMS MODIFICATION REQUEST message are problematic in that they are unable to send information about cells.
Patent document: JP-A No. 2004-312750